The invention generally relates to compositions and methods associated with the storage of red blood cells (RBCs). In particular, it relates to an improved RBC storage composition and processes and applications thereof.
The ability to store and preserve red blood cells (RBCs) for later re-infusion into patients is a relatively recent technological development that was the harbinger to modern surgical practice. Such preservation is scientifically tricky and the steps to achieving longer storage duration and higher quality re-infused red blood cells have been incremental. As soon as they are collected from a donor, red blood cells begin to die as they coagulate, starve, lose ATP, 2,3-DPG, membrane surface area and integrity, and hemoglobin (Hb). Rous & Turner in 1916 and Robertson in 1917 first demonstrated successful whole blood storage. Acid-citrate-dextrose (ACD, 1943), comprising citrate as an anti-coagulant and dextrose as the sole nutrient utilized by red blood cells, and Citrate-phosphate-dextrose solution (CPD, 1957), adding phosphate as a metabolic source and for membrane retention, were subsequently approved for 21-day storage of whole blood. CPD with adenine (CPDA-1, 1979) was later introduced and used for extending the shelf life of stored whole blood and packed RBCs for up to 5 weeks.
Initially, storage compositions were designed to be acidic to prevent the caramelization of the glucose during the heat sterilization performed in the final production step. In the 1950s, adenine was discovered to be useful as an additive and replaces the adenine lost by deamination. In the 1970s it became desirable to remove the plasma from the collected whole blood for platelets and for the manufacture of plasma derivatives. This, however, led to a reduction in the percent recovery of the resulting “packed RBC.”
To circumvent this, compositions known in the art as additive solutions (AS) were developed to restore volume, nutrients, and other useful RBC stabilizers. Additive solution compositions for the preservation of red blood cells (RBCs) after their separation from whole blood are intended to be tailored specifically to the needs of RBCs. The development of certain additive solutions extended RBC storage to 6 weeks in 1981. Red blood cells (RBCs) stored in these solutions, however, undergo steady deterioration after about 6 weeks as determined by the inability of 75% of such cells to survive in the circulation for 24 hours after re-infusion back into the human donor. It has been observed that during continued refrigerated storage, glucose is consumed at a decreasing rate, as the concentration of metabolic waste, i.e. lactic acid and hydrogen ions, increases. Such a decrease in the rate of glucose metabolism leads to depletion of adenosine triphosphate (ATP), which directly correlates to the recovery of RBCs when the cells are returned to the circulation. Additive solutions such as Adsol® (AS-1), Nutricel® (AS-3), Optisol® (AS-5), and ErythroSol® were designed to extend the storage of RBCs at 1-6° C. All three ASs currently licensed in the U.S., AS-1, AS-3, and AS-5, contain saline, adenine, glucose and some citrate and/or mannitol as “membrane protectants.” AS-3 also contains monosodium phosphate. Each of the U.S.-licensed ASs meet the licensure requirements for 6-week RBC storage, but fail to achieve 7-week storage. Presently licensed RBC additive solution compositions were developed before the RBC storage lesion (defined herein as the sum of the survival- and/or function-limiting effects of storage on RBCs) was understood to be an apoptotic process.
Almost all of the whole blood collected now is made into components, and the RBC fraction is stored as packed RBCs. For blood drawn into the additive solution systems, RBCs are packed by centrifugation, plasma is removed so that RBCs make up 80% of the volume, and then 100 ml of additive solution is added sterilely. The resulting suspensions have a RBC volume fraction of approximately 55%. RBCs stored in the conventional FDA-approved additive solutions can be stored for only 6 weeks with an acceptable 24-hour in vivo recovery.
To increase the time of acceptable in vivo recovery of RBCs re-infused into patients after a storage period, attempts have been made to improve the additive solutions and storage processes. In “Studies In Red Blood Cell Preservation-7. In vivo and in vitro Studies With A Modified Phosphate-Ammonium Additive Solution,” by Greenwalt et al., Vox. Sang. 65:87-94 (1993), the authors determined that an experimental additive solution (designated EAS-2) containing (in mM): 20 NH4Cl, 30 Na2 HPO4, 2 adenine, 110 dextrose, 55 mannitol, formulated at a pH of 7.15, is useful in extending the storage shelf-life of human RBCs from the current standard of 5-6 weeks to an improved standard of 8-9 weeks. However, packed RBCs stored in EAS-2 were not directly infusible but required the removal of the supernatant with a washing step prior to transfusion due to the presence of ammonium in the additive solution.
In “Studies in Red Blood Cell Preservation-8; Liquid Storage of Red Cells in Glycerol-Containing Additive Solution,” Vox. Sang. 67:139-143 (1994), Greenwalt et al. described an additive solution (designated EAS-25) that allowed 73 percent recovery of packed red cells after nine weeks. However, the resulting RBC units contained about 1 percent glycerol and thus, are not safe for transfusion in humans in large amounts.
In “Extending the Storage of Red Cells at 4.degree. C.,” Transfus. Sci. 15:105-115 (1994) by Meryman et al., acceptable viability of RBCs stored in very dilute suspensions at low hematocrit for as long as 27 weeks were demonstrated. However, such stored RBC suspensions were not acceptable for direct infusion due to their high content of potassium and ammonia and their low volume fraction of RBCs. The 5 L of solution for 200 mL of RBC required to produce his observed beneficial effects were not clinically practicable.
With respect to approved and commercially available products, the additive solutions presently licensed in the U.S. work for only about 6 weeks with an average recovery of about 80%. Two additive solutions presently licensed in Europe work for about 7 weeks with an average recoveries of 77% (ErythroSol from Baxter Healthcare, La Chatre, France) and 75% (PAGGS mannitol from Maco Pharma). Novel solutions recently described by Kurup et al. (Vox Sang 2003: 85:253-261) may be expected to have shorter storage times because of the lower ATP concentrations.
In response to the deficiencies in these prior findings, the present inventors developed lower volume disodium phosphate-containing alkaline experimental additive solutions (EASs) that partially neutralize the effect of collecting blood into acidic anticoagulant solutions such as CPD (citrate-phosphate-dextrose), and showed that these EASs improved RBC ATP concentrations, reduced hemolysis, and appeared to decrease RBC membrane morphological changes and loss (see U.S. Pat. Nos. 6,150,085 and 6,447,987 to Hess and Greenwalt, the complete disclosures of which are fully incorporated herein by reference). Various EASs were shown to support between 9 and 12 weeks of storage. Although these EASs yielded superior performance results, they contained sodium chloride and were formulated to require a relatively large volume resulting in greater dilution of the stored RBC, thus increasing the risk of hemodilution in multiply transfused patient recipients. In addition, the presence of sodium chloride created a solubility limit on the amount of buffering salts and phosphates that the system could sustain at desirable volumes.
Increased duration of RBC storage remains an important consideration during periods when demand is high but intermittent, such as during wartime, and for geographical regions that require transfusable blood but only on an inconsistent and sporadic basis. In fact, given the current level of reported waste due to expiration of the safe storage period prior to realization of a demand in general, increasing the duration of time that RBCs may be safely stored is an ongoing ubiquitous concern.
Thus, there is a need for RBC storage compositions formulated to retain or enhance recovery and performance benefits in the lower volumes of conventional additive solutions. There is a continuing need in the blood storage and transfusion art for improved RBC storage that results in longer storage duration, better recovery percentage, and improved physiological functioning of the transfused RBC. Consequently, there remains a need for improved RBC storage compositions and processes of manufacture thereof. There is also a continuing need for additive compositions which allow the RBC suspension to which the composition is added to be directly infused into humans, and which permit an acceptable post-infusion recoverability of viable RBCs possessing enhanced physiological functioning capabilities and lower rates of clearance from the infused patient's circulation.